The object of the present invention is to provide important improvements in weft feeding devices for weaving looms, of the type in which the drum around which the weft yarn winds to form a reserve is held stationary, and the turns of said reserve are wound thereon by a rotating reel and are moved forward, mutually spaced, by suitable means.
As is known, it is important in such weft feeding devices to be able to easily check the yarn reserve being wound on the drum and to automatically regulate the winding speed of the turns of said reserve, according to the amount of yarn drawn from the loom.
On weft feeding devices with advancement by adjacent turns, the yarn reserve can be easily checked by using photoelectric cells fixedly connected to the body of the device. These sensors generally comprise a sending element and a receiving element, positioned so that the luminous beam sent by the first element can be received by the second element through reflection from a reflecting element on the winding drum. The presence of yarn reduces the amount of light reflected by the reflecting element positioned on the winding drum, consequently varying the electric signal generated by the receiving element. Said signal can be conveniently used as a pilot signal to run the motor at the desired speed.
On weft feeding devices with advancement by spaced turns (this type of device is preferred, as it allows obtaining a more uniform tension in the various turns being wound, thereby making the evenness of the reserve less strictly tied, than in weft feeding devices with advancement by adjacent turns, to the various motor speeds), it has up to date not been possible to read and check the yarn reserve with the previously described photoelectric methods, because of the considerable spacing between the turns, which makes the operation unsteady and unreliable, especially due to the possible presence of dust gradually settling on the transparent protection element--made of glass or other material--which delimits the optical member of the photoelectric cells.
U.S. Pat. No. 4,638,840 proposes to cause the turns gradually to approach each other, until they become adjacent close to the outlet end of the winding drum. This overcomes the heretofore mentioned difficulties, by operating as in the previously specified arrangement with adjacent turns; nonetheless, especially when working with fine yarns, this arrangement again involves the drawbacks of weft feeding devices with advancement by adjacent turns (particularly the possible overlapping of the turns).